RE: LGWR, EMC or app cursors?
Date: Mon, 14 Oct 2019 10:22:02 +0000
Message-ID: <34306_1571048537_5DA44C59_34306_5990_1_8b8c71d762604235a3430e763a9918f1_at_vontobel.com>
“The storage folks are assuring me that there are no issues at that level and that any shared resources are NOT seeing the same thing. I have to take their word for it.”
Ø You don’t have to take their word for it – you can measure it instead. Mind that the IO stack consists not only of the storage device, but it also contains the components on the server, like OS kernel, multi-pathing drivers, HBA card and HBA drivers. In the case of a bug, some of these components might introduce latencies not visible to the storage admin, as she typically measures the response times on the storage box itself. For example, I was observing the delays of up to several seconds due to OS bugs and the latencies up to 500ms due to inefficiencies of the HBA drivers algorithms. When I once hit a problem similar to yours, I found a way how to triage whether the storage box (including the HBA) are being a part of the problem: https://nenadnoveljic.com/blog/emulex-hba-driver-performance-measuring-latency/ . While the scripts described in the blog post mentioned are completely OS and HBA product dependent, the main idea is transferable across the platforms: calculate the time difference between the fiber-channel-driver-packet-transport and fiber-channel-packet-driver-unit function calls.
Best regards,
Nenad
https://nenadnoveljic.com/blog/
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-- http://www.freelists.org/webpage/oracle-lReceived on Mon Oct 14 2019 - 12:22:02 CEST